This invention relates generally to determining position by electromagnetic radiation. More particularly, the invention relates to an improved system for using sensed position data to maintain a desired distribution of machines.
As the world becomes a more crowded and busy place, there are an increasing number of machines, on land, on sea and in the air. The machines perform a variety of functions and many are man driven vehicles. For example, fleets of taxis or police vehicles are examples of machines which may number in the hundreds in a large city. It would be desirable to manage the distribution of these machines across the city so that they maintain a desired distribution. The desired distribution of machines may be for a variety of purposes such as maintaining a minimum wait time in the event of a call for service. The desired distribution need not be uniform across the city for example as certain areas may require greater service or experience greater call volume.
The Global Positioning System (GPS) is currently the most precise positioning system generally available to the general public and has significantly dropped in price in recent years. The GPS comprises a network of 24 satellites orbiting the earth. Each satellite transmits a ranging signal modulated on a 1.575 Ghz carrier. By monitoring the signal from a plurality of satellites, a GPS receiver can determine its position, i.e. latitude, longitude and altitude, to an accuracy of about 100 meters. In general, this degree of accuracy would be attained if signals from three or four of the GPS satellites were received. More accurate GPS signals are available to the military. Differential GPS, also available to the public, is more accurate than standard GPS, but requires an additional land based transmitter and special permission from the government.
Many of the uses for GPS-based systems known to the Applicants are in the realm of mapping or collision avoidance applications. Notably one such GPS-based system is taught by xe2x80x9cTraffic Alert and Collision Avoidance Coding Systemxe2x80x9d, U.S. Pat. No. 5,636,123 to Rich et al. In the Rich system, the airspace is divided up into a grid of volume elements. A collision avoidance signal is transmitted wherein the carrier signal is modulated by a psuedonoise code which is function of the volume element in which the aircraft is located. Each aircraft only tracks collision avoidance signals from vehicles in its own and immediate surrounding cells. Based on the calculated paths of the aircraft, a warning of an impending collision can be provided to the pilot.
The Applicants have proposed an improved tracking and collision avoidance system in xe2x80x9cTime Multiplexed Global Positioning System Cell Location Beam Systemxe2x80x9d Ser. No. 09/239,335 Attorney Docket No. AT9-98-870 filed the same day as the present application, is commonly assigned and is hereby incorporated by reference. Although the invention described in the incorporated application does not address the problems of maintaining the distribution of machines in a stationary environment, it does share an overall cell structure with the preferred embodiment of the present invention.
This invention solves these and other important problems.
A method for maintaining a desired distribution of machines with respect to a stationary map is disclosed. Each machine determines its location via a global positioning system calculation. Next, the machine determines a cell corresponding to the determined location. Each machine broadcasts a message at a time slice allocated for the cell. A central control center receives the broadcasted messages from a plurality of machines and uses the received broadcasted messages to determine the locations of the plurality of machines. It then matches the determined locations of the machines against a desired distribution of machines. Responsive to a finding that the determined locations do not adequately match the desired distribution, the central command center issues commands to respective machines to bring the machines into compliance with the desired distribution.